Truck Maintenance With A Grease Gun - Willies WorkbenchPosted in How To: Tech Qa on July 1, 2002 0) (
I get a lot of good-natured kidding over my obsession with preventative maintenance. Perhaps I am just a bit anal on the subject. Be it so, oil and grease are cheap commodities when it comes to maximizing the life of your rig. For instance, one of my "maintenance things" is to crawl under my Jeep after a day of trail running with grease gun in hand and hit every zerk fitting. Most likely it's not necessary to do every day, but doing it provides an excuse to do a hands-on look at steering and driveline components. Fifteen minutes of time spent checking these things could make the difference on finding a problem that may make for a tow home if not remedied.
Slip yokes and U-joints working beyond design angles need special attention. Whenever I lube any fitting, I'm sure to have several paper shop towels in hand because I like to force in grease until I see new, clean grease coming out of the joint. On a U-joint, I make sure that grease is coming out all four caps. If it doesn't come out of a bearing cap, it means it's not going in, so it's time to find out why, even if this means you have to take the time to disassemble the U-joint. Sometimes all that's necessary is to reposition the U-joint by rotating the shaft 180 degrees.
What grease to use? Or are all greases the same? Well, yes and no. Most automotive greases are soap-based and in 80 percent or so the soap is made from lithium. However, it could be made from sodium, calcium, or aluminum. The soap is nothing more than a carrier agent to hold the oil and various additives that make up what's called grease. Soap, just like the stuff you wash the grease off your hands with, is made by the chemical reaction that neutralizes a fatty acid and a base.
One thing you don't want to do is mix grease made from two different types of soaps. When mixed together, they will cause the oil to fall out of suspension. This is the same thing that happens when you use a waterless soap to clean your hands.
To the soap, a base stock oil is added, be it of synthetic or petroleum nature. Certain additives, such as zinc for extreme pressure needs, molybdenum as a friction modifier, and even some silicones or other types of hydrophobic material to repel moisture, are combined to form the grease.
Grease specifications are controlled by the National Lubricating Grease Institute. No, I am not making that up. For instance, the thickness (not to be confused by viscosity) is measured on a scale which ranges from #000 to 6. Generally, an NLGI #2 is the stuff you and I use. On that tube of grease you'll also see letters such as GC-LB. The first two letters mean it's suitable for high-temperature usage in wheel bearings on disc-brake vehicles and the second group of letters mean it's a general chassis lubricant with resistance to water. The deeper into the alphabet the second letter of each group, the better the grease.
A GC-LB grease has a lubricating range from - 40 to +400 degrees Fahrenheit. Sometimes you may find a temperature listed as a dropping point. This is the temperature that the oil falls out of suspension within the soap. Generally speaking, to leave room for margin of error this temperature should be approximately 100 degrees higher than maximum operating temperature. For instance, under certain circumstances the grease in wheel bearings may reach above 300 degrees Fahrenheit and a high-angle U-joint may see 200 degrees Fahrenheit, both well within our GC-LB rating. You may also find on the label the words "Timken Ok Load." Without going into the complexity of this testing, just keep in mind any number over 60 is good and over 80 is excellent.
As you can see, grease has to have a multitude of properties in order to do its job. These include low temperature stability, resistance to solid material and moisture intrusion, ability to maintain its viscosity, withstand shock loading, provide a barrier against friction, resist against being thrown out by centrifugal force, have a high channeling point (temperature at which lubrication ceases), and provide oxidation stability.
Next time you grab that grease gun, give some thought to what grease you're using, and why.